Metabolism of endogenous and xenobiotic aldehydes by rainbow trout (Oncorhynchus mykiss) liver fractions
Aldehyde dehydrogenase (ALDH) specific activity was measured in crude homogenates, post-mitochondrial supernatants, cytosolic and microsomal fractions of trout liver, using a number of endogenous and xenobiotic aldehydes and both NAD+ and NADP+ as co-factors. All the activity found in the crude homogenate could be accounted for by the sum of the cytosolic and microsomal activities. Highest activities were found with the medium chain length substrates hexanal and nonanal in all fractions. The α,β-unsaturated aldehydes, (E,E)-2,4-nonadienal-1-al, and trans, trans-2,4-decadienal, were also good substrates for both fractions, while the hydroxylated α,β unsaturated trans-4-hydroxy-2-nonenal was a good substrate only for the microsomal fraction. Short chain and aromatic xenobiotic substrates were metabolized at much lower rates, and only the microsomal fraction was effective against acetaldehyde, acrolein, and benzaldehyde. Neither fraction metabolized 2,5-dihydroxy benzaldehyde. NAD+ was the preferred co-factor for most substrates. Apparent affinity (Km) for hexanal and nonanal in the cytosolic fraction were comparable to that found in rats, but the theoretical maximal velocity (Vmax) for these substrates, and the specific activities for the other substrates, were much lower than found in mammals. The biochemical results suggest that trout are well adapted to detoxify products of endogenous lipid peroxidation, but are poorly adapted to detoxify xenobiotic aldehydes. In another study with carcinogen-fed fish, ALDH distribution was evaluated histochemically in cryostat sections. In control trout, ALDH was uniformly distributed without an apparent zonal pattern. However, in hepatic tumors, ALDH was apparently induced with hexanal, nonanal, and propionaldehyde giving the strongest reaction products; other substrates also reacted, but with much lower sensitivity. © 1990.
Parker, LM; Laurén, DJ; Cooke, JB; Hinton, DE
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